In recent years, apparatuses that measure eye movements have attracted attention. If eye movements can be measured, such measurement can be applied to a visual field test, or, e.g., a tomographic imaging apparatus for a fundus, which acquires images with higher precision, enabling more accurate fundus diagnosis.
For eye movement measurement methods, various techniques, such as the corneal reflection (Purkinje image) method or the search coil method, have been known. Among them, a method in which eye movements are measured from fundus images has been studied as a method that is easy and less stressful for test objects.
In order to measure an eye movement with high accuracy from fundus images, it is necessary to extract a characteristic image from a fundus image, search for and detect the characteristic image in an object image and then calculate the amount of movement of the characteristic image. Among them, the step of extracting the characteristic image is important from the perspective of stability, accuracy and reproducibility of eye movement measurement. For a characteristic image in a fundus image, e.g., a macula or an optic papilla (hereinafter referred to as “papilla”) is used. Also, because, e.g., an affected eye often has a defective macula or papilla, blood vessels may be used for a characteristic image in a fundus image. For a method for extracting a characteristic image of blood vessels, various methods are known. For example, Patent Literature 1 discloses a method in which the number of blood vessels and whether or not blood vessels exist in a center portion of a filter set in a fundus image are determined from average values of pixel values in an outer peripheral portion of the filter to determine whether or not a blood vessel crossing part exists in the filter region.